Fix rst errors in README

This fixes some rst formatting errors in the README file. The
readme is used as the package long description on pypi, and
they have recently enabled some checks that cause package
upload errors if there are formatting issues with the rst
content.
Change-Id: I3ff7a509c2b875606c985c87b61a63c5e15c1bda
(cherry picked from commit be83eae483)